In recent years, mobile communication terminals such as a portable telephone and a mobile telephone have been widely used, and various kinds of multiple access methods have been developed for use in such mobile communication systems. Among them, a CDMA (Code Division Multiple Access) method has been employed in portable telephones and others because it has high quality reception capability through the exploitation of multipath fading, and can achieve a high utilization efficiency of radio resource (can increase a subscriber capacity).
FIG. 8 is a schema which shows that the mobile station can receive a number of radio waves transmitted from adjacent cells via multiple propagation paths (multipath). In general, a plurality of base stations (BS1–BS5) are arranged regularly, and cells of the base stations form a regular polygon if these base stations are arranged to cover a service area with as high a electric field as possible, as is well known and shown in FIG. 8. When a mobile communication terminal (MS) performs the cell search, it receives a plurality of radio waves from respective base stations, and additionally receives radio waves (multipath), which are transmitted from various base stations, and are shifted in timing from each other due to wave reflection and diffraction. This multipath is not necessary, and therefore is deleted during the cell search operation by an appropriate manner.
A stepwise search method has been known as a fast cell search method. FIG. 9 shows a processing procedure for detecting and deleting multipath components in the stepwise search method. First, slot timing for those including multipath components is detected (short-period detection) (S101). Detection of slots is performed by detecting search codes of the slots. By detecting the frame timing code, the frame timing is detected (long-period detection), and further the code group is detected (S102).
In addition to the code group, the candidate codes which belong to the group is further evaluated (S103), and finally a spread codes is identified. Information such as spread codes, which is required for recognizing the multipath, is stored in a memory 110 (S104). In this manner, the multipath is recognized based on the information of code and timing stored in memory 110, and the multipath is deleted from the obtained information (S105). The information, from which the multipath is deleted as described above, is decoded so that an amount of decode processing is reduced, and fast cell search can be achieved.
However, the multipath is deleted after all the slot timing, frame timing and codes for one slot are detected and stored in memory 110. This results in a problem that the time required for the entire cell search cannot be reduced.
The invention has been developed for overcoming the above problem, and a first object of the invention is to provide a mobile communication terminal allowing fast cell search.
A second object of the invention is to provide a mobile communication terminal allowing accurate identification of spread codes.
A third object of the invention is to provide a communication method allowing fast cell search.
A fourth object of the invention is to provide a communication method allowing precise identification of spread codes.